Permanent waving and straightening of hair are common techniques for beautifying hair or fur by permanently forming or setting the hair or fur into a desired configuration. Various techniques have been practiced for many years in the hair and fur industries, such as in hair salons, and in the home practiced by an individual.
Hair and fur is comprised of keratin, which is a polyamide cross-linked by disulfide bonds. The disulfide bonds are responsible for the hair or fur being maintained in a particular configuration. In a conventional hair waving or straightening process, the hair is first softened or relaxed by breaking the disulfide bonds in the keratin with a reducing agent and then hardening the hair or fur in the desired configuration by stopping the reduction reaction and restoring or reforming disulfide bonds by applying an oxidizing agent, generally referred to in the art as a neutralizer.
Dissolved salts and esters of thioglycolic acid and aqueous solutions of sulfites and/or bisulfites have gained wide acceptance as the preferred agents for reducing keratin disulfide bonds. The most common reducing agents in the professional market are the thioglycolates, including thioglycolate, dithioglycolate, thioglycolic acid and its ester, glyceryl monothioglycolate or GMT. Toni Silk Wave, a product of the Gillette Company, Boston, Mass. and Ogilvie Body and Styling Wave, a product of Ogilvie Products, Inc., Montvale N.J., are examples of thioglycolate systems known in the art. Toni Silk Wave contains 0.7N thioglycolic acid at pH 9.3; Ogilvie's Body and Styling Wave contains 1.0N thioglycolate and 0.4N dithioglycolate, and has a pH of 9.3.
The sulfite/bisulfite solutions are sometimes used by the professional market, but are more common for use at home by individuals because of their relatively gentle action and general absence of odor. Generally, sulfite solutions are comprised of ammonium sulfite and ammonium bisulfite in a molar ratio of about 1:1. Rave.RTM. Performance Perm is one example of an ammonium sulfite/bisulfite reduction system known in the art. Rave.RTM. is an ammonium sulfite/bisulfite mixture containing 1.5N sulfite and 12% to 14% urea, and having a pH of 7.3.
It is recognized by those skilled in the art that keratin disulfide bonds are represented as "KSSK", wherein K represents keratin moieties and SS represents the disulfide bond. The reaction of a sulfite with keratin causes the disulfide bonds to be split into two fragments, present in an essentially 1:1 stoichiometric ratio--reduction to a mercaptan or thiol (KSH) and oxidation to a thiosulfate (KSSO.sub.3.sup.-) commonly called a Bunte salt --as indicated in the following equation: EQU KSSK+HSO.sub.3.sup.- .fwdarw.KSH+KSSO.sub.3.sup.- (I)
Thioglycolic acid is a thiol, which generally exists as the anion, OCCH.sub.2 SH, at the pH values commonly used in practice. The reaction of thioglycolic acid with keratin differs from the sulfite reaction and results in several end products as noted below. Keratin reaction with thioglycolic acid may be represented as follows: EQU KSSK+2RSH.fwdarw.2KSH+RSSR (II)
wherein RSH is thioglycolic acid and RSSR represents the disulfide of thioglycolate. The laws of chemical equilibrium demand that the actual products of this reaction also include, in variable stoichiometric amounts, KSSR, a hybrid disulfide of keratin and thioglycolate. Therefore, KSSK, KSSR, RSSR, RSH and KSH will be present in the hair or fur after treatment with thioglycolic acid. Thorough rinsing will remove much of the RSSR and RSH from the hair or fur. Any product containing KS- is essentially fixed within the hair or fur.
Several oxidizing or neutralizing agents are well known in the art, including aqueous hydrogen peroxide and aqueous sodium bromate. However, when sulfite systems are used to reduce the disulfide bonds, conventional oxidizing agents do not reverse the disulfide splitting reaction and only the thiol fragments are reformed to disulfide, as shown in Equation III: EQU 2KSH+H.sub.2 O.sub.2 .fwdarw.KSSK+2H.sub.2 O (III)
Bunte salt is very resistant to oxidation and does not react with oxidants to reform keratin disulfide bonds. Consequently, only one-half of the disulfide bonds reduced by sulfite systems are restored and the resulting hair or fur configuration is weak, of poor durability, and the overall tensile strength of the hair or fur is impaired.
When thioglycolate systems are used to reduce the keratin disulfide bonds in the hair or fur, the thiol fragments are restored to disulfide as in Equation III when reacted with an oxidizing agent. Those fragments existing as KSSR, however, cannot be reformed by an oxidative process. Moreover, the greater the quantity of KSSR formed, the lesser the holding strength of the desired configuration of the hair or fur, the weaker the tensile strength of the hair or fur, and the greater the hair or fur is open to damage.
A high percentage of KSSR resulting from the reduction of the disulfide bonds has long been a problem in the art. For example, if the thioglycolate concentration is too high, or if the reduction agent is permitted to react for too long a time, the fraction of keratin converted to KSSR can increase to an unacceptable level. This condition, when it occurs, is generally referred to as "overprocessing."
Attempts in the prior art to avoid the problems inherent with conventional neutralizers include use of simple and amino salts in conjunction with an organo-carbonate promoter as neutralizer in sulfite systems. See Japanese Patent Application No. 49-101743 of Okauchi. However, such systems cause sulfite precipitation--an undesirable reaction in hair care technology, which is substantially avoided in this invention.
In view of the serious deficiencies and inefficiencies of the prior art, it is desirable to neutralize hair relaxed or softened by either a thioglycolate or a sulfite in such a way so as to have reformation of substantially all the keratin disulfide bonds while substantially avoiding precipitation. A water soluble, safe, non-toxic neutralizer is desirable.